钻石与水悖论
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钻石与水悖论首次由亚当·斯密在他的著作《国富论》里提出，也称作价值悖论。此一理论在台湾教科书中常被称作“钻石与水的矛盾”，即是中国俗谚中的：物以稀为贵。
众所周知，钻石对于人类维持生存没有任何价值（使用价值），然而其市场价值（价格）非常高。相反，水是人类生存的必需品，其市场价值（交换价值）却非常低。这种强烈的反差就构成了这个悖论。为什么会有这样的现象呢？若不考虑市场上的其他因素，沙漠地区的水比钻石贵，或者是需求面的因素。就供给面来说，水的数量非常大，且几乎随处可见（如果不考虑荒漠干旱地区，地球上几乎处处都有水，包含大气层中的水汽）；而钻石呢，是蕴藏在地表底下，且必须经过时间与适当的条件产生（如果不考虑人工钻石而单纯考虑自然钻石），供给非常的少，因此水供给大，而钻石供给少，故会产生这样的现象。
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劳动价值论
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主条目：劳动价值论
亚当·斯密通过阐明价值有两种不同的意思来解释这个悖论：
- 应当注意，价值一词有两个不同的意义。它有时表示特定物品的效用，有时又表示由于占有某物而取得的对他种货物的购买力。前者可叫做使用价值，后者可叫做交换价值。使用价值很大的东西，往往具有极小的交换价值，甚或没有；反之，交换价值很大的东西，往往具有极小的使用价值，甚或没有。例如，水的用途最大，但我们不能以水购买任何物品，也不会拿任何物品与水交换。反之，钻石虽几乎无使用价值可言，但须有大量其他货物才能与之交换。[1]
此外，他又解释了交换价值由劳动决定：
- 任何一个物品的真实价格，即要取得这物品实际上所付出的代价，乃是获得它的辛苦和麻烦。[2]
因此，斯密否认了价格和效用之间的必然联系。价格在本观点中，而不是从消费者的角度，和生产要素（即劳动）相关。[3]劳动价值理论的支持者们认为这种说法自相矛盾。
劳动价值论在西方主流的经济学中不再流行，已被边际效用理论替代。
边际主义
凯恩斯经济学对此做出了解释，凯恩斯认为物品的价格不光是由它的价值决定，还由边际价格决定的，即在当前情况下再增加一份该物质所需花费的价格就是该物质的价格。水虽然很宝贵,可是水在地球上很多，于是它的价格相对于数量的边际价格就很低，而钻石刚好相反，因此水的价格很便宜，钻石的价格很贵。[4]
基于主观价值论的边际效用论认为， the price at which an object trades in the market is determined neither by how much labor was exerted in its production, as in the labor theory of value, nor on how useful it is on a whole (total utility). Rather, its price is determined by its marginal utility. The marginal utility of a good is its least important use to a person. The reasoning goes like this. If someone possesses a good, he will use it to satisfy some need or want. Which one? Naturally, the one that takes highest-priority. Eugen von B?hm-Bawerk illustrated this with the example of a farmer having five sacks of grain.[6] With the first, he will make bread to survive. With the second, he will make more bread, in order to be strong enough to work. With the next, he will feed his farm animals. The next is used to make whisky, and the last one he feeds to the pigeons. If one of those bags is stolen, he will not reduce each of those activities by one-fifth; instead he will stop feeding the pigeons. So the value of the fifth bag of grain is equal to the satisfaction he gets from feeding the pigeons. If he sells that bag and neglects the pigeons, his least productive use of the remaining grain is to make whisky, so the value of a fourth bag of grain is the value of his whisky. Only if he loses four bags of grain will he start eating less; that is the most productive use of his grain. The last bag of grain is worth his life.
In explaining the diamond-water paradox, marginalists explain that it is not the total usefulness of diamonds or water that matters, but the usefulness of each unit of water or diamonds. It is true that the total utility of water to people is tremendous, because they need it to survive. However, since water is in such large supply in the world, the marginal utility of water is low. In other words, each additional unit of water that becomes available can be applied to less urgent uses as more urgent uses for water are satisfied. Therefore, any particular unit of water becomes worth less to people as the supply of water increases. On the other hand, diamonds are in much lower supply. They are of such low supply that the usefulness of one diamond is greater than the usefulness of one glass of water which is in abundant supply. Thus, diamonds are worth more to people. Therefore, those who want diamonds are willing to pay a higher price for one diamond than for one glass of water, and sellers of diamonds ask a price for one diamond that is higher than for one glass of water.
对悖论的批评
George Stigler has argued that Smith's statement of the paradox is flawed, since it consisted of a comparison between heterogeneous goods, and such comparison would have required using the concept of marginal utility of income. And since this concept was not known in Smith's time, then the value in use and value in exchange judgement may be meaningless:
The paradox—that value in exchange may exceed or fall short of value in use—was, strictly speaking, a meaningless statement, for Smith had no basis (i.e., no concept of marginal utility of income or marginal price of utility) on which he could compare such heterogeneous quantities. On any reasonable interpretation, moreover, Smith's statement that value in use could be less than value in exchange was clearly a moral judgment, not shared by the possessors of diamonds. To avoid the incomparability of money and utility, one may interpret Smith to mean that the ratio of values of two commodities is not equal to the ratio of their total utilities. Or, alternatively, that the ratio of the prices of two commodities is not equal to the ratio of their total utilities; but this also requires an illegitimate selection of units: The price of what quantity of diamonds is to be compared with the price of one gallon of water?
—George Stigler, The development of Utility Theory. I [5]
参见
- 享乐主义的悖论
资料来源
- ^ 斯密, 亚当（1776年）．“第一篇，第四章 货币的起源及其效用”，国富论． 于2006四月参阅．
- ^ 斯密, 亚当（1776年）．“第一篇，第五章 论商品的真实价格与名义价格或其劳动价格与货币价格”，国富论． 于2006七月参阅．
- ^ Dhamee, Yousuf(1996?), 亚当·斯密与劳动分工 accessed 09/08/06
- ^ 经济学，张清溪等著，台湾台北，2002年。
- ^ Stigler, George (1950). The development of Utility Theory. I. Journal of political economy 58(4), p 308.
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